Ion beam exclusion paths on the target surface to optimize neutron beam performance

ABSTRACT

Embodiments of systems, devices, and methods relate to exclusion of ion beam paths on the target surface to optimize neutron beam performance. A particle beam is directed along an axis so that the particle beam is incident on a target positioned on the particle beam axis. The target has a scannable surface extending over an area substantially orthogonal to the axis. The particle beam is scanned across the scannable surface of the target along a first path having a first flux. The particle beam, having a second flux, is scanned across the scannable surface of the target along a second path that is within an exclusion area of the target.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. 119 to ProvisionalApplication No. 63/315,865, filed Mar. 2, 2022, which is incorporated byreference.

FIELD

The subject matter described herein relates generally to systems,devices, and methods for determining and directing an ion beam path on atarget surface, and more particularly determining and directing an ionbeam path on a target surface for neutron beam generation.

BACKGROUND

Boron neutron capture therapy (BNCT) is a modality of treatment of avariety of types of cancer, including some of the most difficult types.BNCT is a technique that selectively aims to treat tumor cells whilesparing the normal cells using a boron compound. The boron compoundallows for efficient uptake by a variety of cell types and selectivedrug accumulation at target sites, such as tumor cells. Boron loadedcells can be irradiated with neutrons (e.g., in the form of a neutronbeam). The neutrons react with the boron to eradicate the tumor cells.

Neutron beams for BNCT can be generated by irradiating a suitable targetwith an ion beam, such as a proton beam. The ions react with nuclei inthe target to emit a beam of neutrons that can be used for BNCT.Exposure of a shadowed section of a target to an ion beam can reduce theefficacy of the neutron beam, negatively impacting the treatment.

SUMMARY

Example embodiments of systems, devices, and methods described hereinrelate to a selection of a profile for scanning a (charged) particlebeam (e.g., a proton beam) across a target surface avoiding unfavorablesections (exclusion regions) of the target that are shadowed by thecooling tubes or areas of the particle beam shaping assembly that haveadditional geometric perturbations from diagnostics or controls. In someimplementations, a beam path across the target surface forms a firstpattern. The pattern, also called a fundamental pattern or cycle, isrepeated one or more times at different radial orientations from thefirst instance of the pattern to form a scanning profile. Here, a“radial” orientation refers to an azimuthal or, alternatively,circumferential direction in a cylindrical coordinate system. Theembodiments include at least two instances of a first beam patternradially offset from each other. The various instances of the beampattern can be offset by a constant amount such that the scanningprofile includes instances of the pattern clocked at regular radialintervals. The embodiments are based on computational modellingconfigured to improve thermal performance and particle loading, amongother advantages. For example, computational modelling can allow forselection of beam scan (or raster) profiles that improve uniformity ofparticle loading on particular sections of a target and/or can allowselection of a scanning profile that reduces (e.g., minimizes) peaktransient temperature of the target. The pattern and intensity of theproton beam can be optimized to preferentially create neutrons ingeometric regions of interest and minimize the number of neutronsproduced in the target that are less desirable. For the current targetand beam shaping assembly design, the raster pattern can be used tominimize neutron production in areas or volumes of the target that areshadowed by system parts (e.g., the cooling tubes) or areas of the beamshaping assembly that have additional geometric perturbations fromdiagnostics or controls. The capability to select a scanning profilethat avoids particular regions of the target allows for flexibility intarget cooling and beam shaping assembly designs, which are coupled withdesired neutron beam performance.

The computational model indicates the thermal effect on a target ofseveral beam parameters, such as the beam's size and shape. Thecomputational model can include a meshed space encompassing optimal andexclusion zones of the target. The mesh is composed of athree-dimensional grid in which the thermal loads on the target aremodeled. The temperature values are obtained by solving aone-dimensional heat transport equation at each “pixel” (element) of thegrid. The one-dimensional heat transport equation is solved for thermaltransport through the depth of the pixel considering that cross talkbetween pixels or lateral heat conduction between pixels is assumed tobe negligible. Numerical approaches used to solve the one-dimensionalheat transport differential equation include finite-element andfinite-difference methods. For either of the finite-element andfinite-difference techniques, the scannable regions and the exclusionzones of the target are represented in a plan view as a portion of thegrid. The grid can have the same unit cell size in each dimension or thesize in each dimension can differ. Resolution can be selected to providethe ability to model beams of different size and structure in line tothe physical capabilities of the system under study. The computationalmodel enables selection of a scan profile that defines a path for theproton beam having a minimum delay between successive exposures of asingle location of the target to the proton beam exceeds a thresholdperiod. The selected profile can define a path based on a trochoid shapeincluding a plurality of lobes. The computational model enables aselection of a profile that has a varying angular frequency of theproton beam between different lobes of the trochoid shape. Thecomputational model enables a selection of a profile that has a varyingangular velocity of the proton beam across the target surface tominimize the time the proton beam is within exclusion zones of thetarget. The computational model enables a selection of a scan profilethat has a varying linear velocity of the proton beam across the targetsurface to minimize the time the proton beam is within exclusion zonesof the target. The computational model enables a selection of anintensity of the proton beam to preferentially create neutrons ingeometric regions of interest and minimize the number of neutronsproduced in exclusion zones of the target. The exclusion zone is notalong the entire outer edge of the target. In some implementations, theexclusion zone is a polygonal shape. In some implementations, theexclusion zone is at asymmetric azimuthal locations about a center ofthe target.

Other systems, devices, methods, features and advantages of the subjectmatter described herein will be or will become apparent to one withskill in the art upon examination of the following figures and detaileddescription. It is intended that all such additional systems, methods,features and advantages be included within this description, be withinthe scope of the subject matter described herein and be protected by theaccompanying claims. In no way should the features of the exampleembodiments be construed as limiting the appended claims, absent expressrecitation of those features in the claims.

BRIEF DESCRIPTION OF DRAWINGS

The details of the subject matter set forth herein, both as to itsstructure and operation, may be apparent by study of the accompanyingfigures, in which like reference numerals refer to like parts. Thecomponents in the figures are not necessarily to scale, emphasis insteadbeing placed upon illustrating the principles of the subject matter.Moreover, all illustrations are intended to convey concepts, whererelative sizes, shapes and other detailed attributes may be illustratedschematically rather than literally or precisely.

FIG. 1A is a schematic view of an example embodiment of a neutron beamsystem in accordance with the present disclosure.

FIG. 1B is a schematic view of an example embodiment of a neutron beamsystem for use in boron neutron capture therapy (BNCT).

FIG. 2A is a perspective view of an example embodiment of a target.

FIG. 2B is a cross-sectional view taken along line 2B-2B of FIG. 2A.

FIG. 2C is a cross-sectional view of another example embodiment of atarget.

FIG. 2D is a perspective rear view of an example embodiment of a targetwith cooling lines.

FIG. 3A is a schematic view of an example of a beam path that forms afirst pattern in accordance with the present subject matter.

FIGS. 3B-3C are schematic views of example beam paths with ellipticaland circular beam cross-sectional profiles, respectively.

FIGS. 4A-4G are example embodiments of scanning profiles having multipleinstances of a beam pattern repeated at different radial orientations.

FIGS. 5A and 5B are examples of computer models including a target inaccordance with the present disclosure.

FIGS. 6A-6D are examples of modeled thermal maps in accordance with thepresent disclosure.

FIGS. 7A-7D are examples of recent path avoidance (RPA) patterns.

FIG. 8 is an example of neutron flux radial distributions based ondifferent proton beam raster patterns.

FIGS. 9A-9O are examples of simulation results in accordance withimplementations of the present disclosure.

FIG. 10 is a flowchart depicting an example process that can be executedin accordance with implementations of the present disclosure.

FIG. 11 is an example system that can be implemented in accordance withthe present disclosure.

FIG. 12 is a schematic illustration of example computer systems that canbe used to execute implementations of the present disclosure.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Before the present subject matter is described in detail, it is to beunderstood that this disclosure is not limited to the particularembodiments described, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present disclosure will be limited onlyby the appended claims.

The term “particle” is used broadly herein and, unless otherwiselimited, can be used to describe an electron, a proton (or H+ ion), or aneutron, as well as a species having more than one electron, proton,and/or neutron (e.g., other ions, atoms, and molecules).

Example embodiments of systems, devices, and methods are describedherein for beam paths of a beam along a target surface of, or used incombination with, a beam system (e.g., including a particleaccelerator). The embodiments described herein can be used with any typeof particle accelerator or in any particle accelerator applicationinvolving production of a charged particle beam at specified energiesfor supply to the particle accelerator. Embodiments herein can be usedin numerous applications, an example of which is as a neutron beamsystem for generation of a neutron beam for use in boron neutron capturetherapy (BNCT). BNCT uses a beam of epithermal neutrons (e.g., with anenergy spectrum within 3-30 kiloelectronvolts) for cancer treatment. Insome implementations, the epithermal neutrons (e.g., epithermal neutronbeams) are generated based on nuclear reactions of protons (e.g., aproton beam) with either a Beryllium target or a Lithium target.

The proton beam can be generated by a particle accelerator, such as atandem accelerator. For example, the tandem accelerator can be anelectrostatic accelerator that employs a two-step acceleration ofcharged particles using a single high voltage terminal. The high voltagecan be used to generate an electric field that is applied to theincoming beam of negatively charged ions to accelerate it towards thecenter of the accelerator. The center of the tandem accelerator can beconfigured to convert the beam of negatively charged ions into a protonbeam in a process of charge exchange. The parameters of the proton beam,such as a beam dimension, a beam shape, and a beam structure can bevaried to optimize usage of particular regions of interest of the targetrelative to localized heating of the target, cooling tubes or areas ofthe beam shaping assembly (BSA) that can include additional geometricperturbations from diagnostics or controls.

For ease of description, many embodiments described herein will be doneso in the context of scanning a proton beam across different regions ofa target to generate a neutron beam for use in BNCT, although theembodiments are not limited to such, and can be applied to scanning ofother charged particle beams, generation of beams other than neutronbeams, and usages outside of BNCT applications. The target can bemaintained in front of fixed cooling tubes, in a fixed (unvarying)position while scanning the proton beam across the target surface.Alternatively, the target can be moved (e.g., rotated) in front of fixedcooling tubes, while the proton beam is scanned across particularregions of the target surface. Both approaches are described herein. Theembodiments pertaining to the scanning (rastering) of charged particlebeams are described primarily in the context of a fixed target havingcooling tubes located behind it; however all such embodiments can beconfigured for use in the approach where the target is moving in frontof fixed cooling tubes and one or more additional geometricperturbations from diagnostics or controls.

FIG. 1A illustrates a schematic view of an example embodiment of asystem 100 for use in BNCT, in accordance with the present disclosure.The system 100 includes a beam system 102 configured to generate aproton beam 104 and a target 196 that is scanned by the proton beam 104to generate a neutron beam 106 that is directed towards a patient 108.The beam system 102 includes a charged particle source 122, a low-energybeamline (LEBL) 190, an accelerator 140 and a high-energy beamline(HEBL) 150. The accelerator 140 is coupled to the low-energy beamline(LEBL) 190 and is configured to accelerate a charged particle (proton)beam. The high-energy beamline (HEBL) 150 extends from the accelerator140 to a target assembly 110 housing a target 196 onto which the chargedparticle beam can be directed. LEBL 190 is configured to transport thebeam from source 122 to the accelerator 140. The accelerator 140 isconfigured to accelerate the beam. HEBL 150 transfers the beam 104 froman output of accelerator 140 to the target 196. In some implementations,the HEBL 150 transfers the beam 104 to the target 196 through a targetchamber of the target assembly 110. The beam 104 can be a negativecharged particle beam or a positive charge particle beam. The target 196can be a device that converts the charged particle beam 104 into anothertype of particle beam 106, such as a neutron beam. The target 196 can bea workpiece, onto which the charge particle beam is directed for aparticle beam 106 configured for a therapeutic purpose, such as anirradiating a tissue of a patient 108. In various configurations ofneutron beam systems (e.g., system 100 described with reference to FIG.1A) there may be parts of the system between the target and the beamoutput (and thus the patient), that can adversely affect the neutronflux output to the patient. For example, the target 196 can be locatedproximal to cooling tubes 130 or in contact with the cooling tubes 130to decrease a temperature of the target 196. In some implementations,one or more diagnostics or control items 132 are located proximal to therear surface of the target 196 potentially generating perturbations ofthe particle beam 106. These parts can be said to shadow the target 196in certain areas, and as such, it can be is desirable to utilize ascanning pattern that seeks to generate relatively less neutron flux inthese areas of the target that are shadowed (e.g., exclusion areas orzones). Numerous scanning patterns can be utilized to accomplish thisrelative reduction of neutron flux generated by the exclusion zones,such as a simple X-Y stepped pattern, as described with reference toFIG. 2D or a simple geometric spiral, as described with reference toFIGS. 7A-7D, though other more simple patterns can likewise be used ifdesired

FIG. 1B is a schematic view illustrating an example embodiment of thebeam system 102 configured as a neutron beam system for use in BNCT. Thebeam system 102 includes a pre-accelerator system 120 forming at least aportion of the LEBL, where the pre-accelerator system 120 serves as acharged particle beam injector, a high voltage (HV) tandem accelerator140 coupled to the pre-accelerator system 120, and a high-energybeamline 150 extending from the HV tandem accelerator 140 to a neutrontarget assembly 110 housing a neutron-producing target 196, as describedwith reference to FIG. 1A. The beam system 102 as well aspre-accelerator system 120 can also be used for other applications, suchas cargo inspection and applications, and is not limited to BNCT.

The pre-accelerator system 120 (also referred to herein as the chargedparticle beam injector or ion beam injector) can be configured totransfer the ion beam from an ion source 122 to an input (e.g., an inputaperture) of the HV tandem accelerator 140. The pre-accelerator system120 can include the ion source 122 (e.g., negative ion source), aturbomolecular pump 124 (e.g., an ion source vacuum chamber for removinggas), a pre-acceleration tube 126, and a pump chamber 128. In someimplementations, the beam source 122 can include a negative ion source.The pre-accelerator system 120 can be configured to provide accelerationof the beam particles to energy levels required for the HV tandemaccelerator 140, and to provide an overall convergence of the negativeion beam to match an input aperture area at an input aperture orentrance of the HV tandem accelerator 140. The pre-accelerator system120 can be configured to minimize or defocus backflow as it passes fromthe HV tandem accelerator 140 through the pre-accelerator system 120 inorder to reduce the possibility of damage to ion source 122 and/or thebackflow reaching the filaments of the ion source 122.

The HV tandem accelerator 140 is powered by a high voltage power supply142 coupled thereto. The HV tandem accelerator 140 includes a vacuumtank, a charge-exchange target, accelerating electrodes, and a highvoltage feedthrough. The HV tandem accelerator 140 can, in someimplementations, accelerate a hydrogen beam to produce a proton beamwith an energy generally equal to twice the voltage applied to theaccelerating electrodes positioned within the HV tandem accelerator 140.The energy level of the proton beam can be achieved by accelerating thebeam of negative hydrogen ions from the input of the HV tandemaccelerator 140 to the innermost high-potential electrode, stripping twoelectrons from each ion, and then accelerating the resulting protonsdownstream by the same voltages encountered in reverse order.

The high-energy beamline 150 can transfer the proton beam from theoutput of the HV tandem accelerator 140 to the neutron-generating target196 in the neutron target assembly 110 positioned at the end of a branch170 of the beamline extending into a patient treatment room.

The beam system 102 can be configured to direct the proton beam to oneor more targets 196 and associated target areas. In someimplementations, the high-energy beamline 150 includes multiple (e.g.,three) branches 170, 180, and 190 configured to extend to multipledifferent patient treatment rooms. The branches 180 and 190 can containtarget assemblies similar to branch 170. The high-energy beamline 150includes a pumping chamber 151, quadrupole magnets 152 and 172 toprevent de-focusing of the beam, dipole or bending magnets 156 and 158to steer the beam towards one or more targets, beam correctors 153,diagnostics such as current monitors 154 and 176, fast beam positionmonitor 155 section, and a X-Y scanning pair magnets 174.

The beam system 102 may employ one or more control systems 1101 withwhich one or more computing devices 1102 may communicate in order tointeract with the systems and components of the beam system 102 (e.g.,neutron beam system 102). In some implementations, the computing device1102 is configured to execute a computational model that enablesselection of a raster profile, as described with reference to FIGS. 6Aand 6B. The computing device 1102 is configured to receive a user inputincluding a selection of one or more parameters of the target scanningprocess. The parameters can define the raster profile including the beampath, the orientation of a shaped beam relative to the scannable surfaceof the target, the beam cross-sectional profile, and the beam velocity.The parameters can define target characteristics, such as rotation ofthe target 196 (e.g., angular velocity of the target). In someimplementations, the computing devices 1102 are configured to receive areal time signal measured by a sensor 121 or a thermal camera 123, whichare used to adjust in real time the raster profile using an adaptablescanning program to avoid local overheating of the target 196 (e.g.,keeping the local temperature below Lithium melting temperature of 180°C.). The one or more thermal sensors 121 can detect localizedtemperature corresponding to a portion of the target. The thermal camera123 can be configured to generate a signal that can be processed togenerate a temperature map of the target 196. The computing device 1102can be configured to process the received input and generate a set ofscanning parameters that are transmitted to the one or more controlsystems 1101 to control the target scanning process that operates the XYscanning pair magnets 174.

The design of the high-energy beamline 150 depends on the configurationof the treatment facility (e.g., a single-story configuration of atreatment facility, a two-story configuration of a treatment facility,and the like). The beam can be delivered to a target assembly 110 (e.g.,positioned near a treatment room having a patient 108) with the use ofthe bending magnet 156. Quadrupole magnets 172 can be included to thenfocus the beam to a certain size at the target. The beam can pass one ormore X-Y scanning pair magnets 174 to be directed according, whichprovide lateral movement of the beam onto the target surface in adesired pattern (e.g., spiral, curved, stepped in rows and columns,combinations thereof, and others). The beam lateral movement can enablegeneration of smooth and even time-averaged distribution of the protonbeam on the target 196, preventing overheating of the target 196 andmaking the particle (e.g., neutron) generation as uniform as possiblewithin the target layer 201 (e.g., lithium layer).

The X-Y scanning pair magnets 174 can be configured to direct the beamto a current monitor 176, which measures beam current. The beam currentvalue, measured by the current monitor 176, can be used to operate asafety interlock. The target assembly 110 can be physically separatedfrom the high-energy beamline volume with a gate valve 177. A functionof the gate valve 177 is to separate the vacuum volume of the beamlinefrom the target 196 during target exchange/loading. In someimplementations, the beam instead of being bent by 90 degrees by abending magnet 156, can be directed straight to the right to enter thequadrupole magnets 152, which are located in the horizontal beamline. Insome implementations, the quadrupole magnets 152 are optional and notincluded in system 100. The beam could be bent by another bending magnet158 to a preset angle, depending on a setting requirement (e.g.,location of a patient or a room configuration). In some implementations,bending magnet 158 can be arranged at a split in the beamline and can beconfigured to direct the beam in one of two directions for two differenttreatment rooms located on the same floor of a medical facility.

FIG. 2A is a perspective view of the target 196 and FIG. 2B is across-sectional view of the target 196 illustrating cooling channels. Inthis embodiment target 196 is disk shaped with a generally circularouter profile. The target 196 generally includes one or more targetlayers 201 supported by a substrate 203. The side of the substrate 203includes channels 204 for a coolant. A scannable surface 210 is presenton target layer 201, which is the surface of target layer 201 that canbe scanned by the proton beam to produce neutrons. The target layers 201include a neutron source layer, such as a layer of lithium, beryllium,or other suitable material that interacts with the proton beam 104 toproduce a neutron flux. The thickness and composition of the one or moretarget layers 201 can vary depending on the properties of the protonbeam and the desired neutron flux. For example, a lithium based targetlayer can have a thickness in a range from about 10 microns (μm) toabout 400 μm. The target layer 201 can be adhered to the substrate 203via a thermal bond.

The substrate 203 can include one or more layers of copper, aluminum,stainless steel, titanium, and/or molybdenum. The target layer 201,including a reactive metal, can form an amalgam with the substrate 203.The characteristics of the target 196 (e.g., layer thickness,composition, and bond type) are associated with an onset of blisteringat particular levels of particle doses per target surface.

Channels 204 can be used to circulate coolant across the backside ofsubstrate 203 during operation of the system 100, in order to dissipateheat produced by absorption of kinetic energy from slowing in substrate203 of the protons that did not participate in the reaction.Alternatively, or additionally, coolant can be provided as a fluidchamber in contact with at least a portion of the substrate 203. Forexample, coolant channels can be formed as capped through-holes thatcross the substrate 203 and define closed fluid passages with a varietyof different geometries (e.g., circular or rectangular cross sections)and dimensions (e.g., cross sectional diameters ranging from about 0.5millimeters (mm) to about 3 mm).

The target 196 can be supported by a support structure (e.g., a shaft111 or a base 112). The support structure can be configured to maintainthe target 196 in a fixed position or to rotate the target 196 clockwise114 or anticlockwise in a vertical plane including a vertical axis 116that is nominally perpendicular to the beam axis. The particle beam 104can be dynamically directed towards the target 196 according to aparticular pattern (e.g., spiral, curved, stepped in rows and columns,combinations thereof, and others) that may change over time. The patterncan be repeated at a given frequency. In some implementations, both thetarget 196 and the beam 104 move relative to the beam axis duringoperation, such that segments of the rotatable target 196 can besequentially contacted by the beam 104 to form a scanning pattern, asdescribed in detail with reference to FIGS. 3-5 and 7 . As a result ofthe interaction of the beam 104 with the target layer 201 (e.g., neutronsource layer), a beam 106 (e.g., neutron beam) is generated and directed(e.g., via a collimator or other beam-shaping structure) towards atreatment area of the patient 108.

FIG. 2C is a cross-sectional view of another example embodiment, wheretarget 196 includes an intermediate layer 202 located between the targetlayer 201 and the target substrate 203. The intermediate layer 202 canreduce the likelihood of blister formation within the target 196 due tothe impingement of the beam. The intermediate layer 202 can be composedof thermally conductive materials that are resistant to blistering, suchas tantalum.

During operation of the beam system 102, the proton beam 104 is directedat scannable surface 210 of target 196. In order to avoid overheating,the proton beam 104 is moved at a rapid rate in two directions (X and Y)across surface 210, which is a process referred to as scanning. The paththat the beam takes across surface 210 determines the amount of heatingthat occurs at different locations across surface 210 and relativedifferences in particle loading on target 196. The beam path can beconformed to the capabilities of the system to cool the target 196 andthe capability of the target 196 to withstand variances in particleloading.

FIG. 2D is a perspective rear view of an example embodiment, where thetarget 196 is located near system parts (e.g., multiple cooling lines130) that can interfere with the resultant particle beam by shadowingthe particle (e.g., neutron) producing region (rear surface) of thetarget 196. In some implementations, one or more of the cooling lines130 overlap a region 254 of the target 196, in the X direction 250 andin the Y direction 252. The region of the target 196 overlapped bycooling lines defines an exclusion zone 254 of the target 196 whereinthe proton beam can be minimized in terms of time exposure and intensityof the proton beam. A region of interest 256 of the target 196 can bedefined as the section of the target outside the exclusion zone 254 ofthe target 196. In some implementations, the region of interest 256 ofthe target 196 can be defined as a U shape that excludes the exclusionzone 254 of the target 196.

These parts can be said to shadow the target in certain areas, and assuch, it can be is desirable to utilize a scanning pattern that seeks togenerate relatively less neutron flux in these areas of the target thatare shadowed (e.g., exclusion areas or zones). Numerous scanningpatterns can be utilized to accomplish this relative reduction ofneutron flux generated by the exclusion zones, such as a simple X-Ystepped pattern 258 or a simple geometric spiral. However, other morepatterns can likewise be used if desired.

FIG. 3A is a schematic view depicting an example pattern 300 formed by apath 301 that a beam takes across surface 210. The outer boundary of thebeam cross-section is indicated by cross-sectional profile 320, which inthis example is circular. Pattern 300 of path 301 is curved withmultiple loops, or orbits, created as the beam proceeds from an outerregion of surface 210 to an inner region and then back again to theouter region. Beam path 301 includes a starting location A and astopping location O. The locations A, O can be the same single locationor different locations. In some embodiments, the starting and stoppinglocations A, O can be the same position or in close proximity to eachother (e.g., adjacent positions, or positions within one beam diameterof each other).

Path 301 starts at location A and proceeds in a counterclockwise (CCW)manner indicated by arrow B. Path 301 continues in an inwardly directedspiral fashion (e.g., with continually decreasing radius) as indicatedby arrows C, D, E, F, G, and H. Arrow H indicates entry of beam path 301into the smallest radius orbit until reaching location I, which marksthe position where the beam path radius transitions from a continuallydecreasing radius to a continually increasing radius. In other words, atlocation I, beam path 301 begins to transition from the inner region ofsurface 210 back towards the outer region. Arrow J indicates the path ofbeam 301 from location I in counterclockwise manner in an outwardlydirected spiral fashion (e.g., with continually increasing radius) asindicated by arrows K, L, M, and N until reaching stopping location O.At this point path 301 has completed a transition from the outer regionto the inner region and back to the outer region of surface 210. A pathwith at least one orbit about a central point, that has a starting and astopping location at the same distance (or radius) from the centralpoint, and that traverses between a minimum distance (or radius) fromthe central point and a maximum distance (or radius) from the centralpoint, is referred to as a cycle. The starting and stopping locationscan be at any distance between (and including) the minimum distance andthe maximum distance. In this case, the single cycle forms a closed loopsuch that stopping location O is substantially at or adjacent tostarting location A.

Pattern 300 can cover a majority of the surface area of the scannablesurface 210 of the target. In this example beam profile 320 is largeenough such that area of surface 210 impinged upon by the beam willoverlap as the beam transitions through each orbit. Stated differently,the width of beam profile 320, measured perpendicular to the directionof travel of the beam, is greater than a distance between adjacentorbits. The pattern 300 is symmetrical along axis 330, such that a firsthalf 332 of pattern 300 is a mirror image of a second half 334 ofpattern 300. The outward to inward portion of path 301 from location Ato location I is a mirror image of the inward to outward portion of path301 from location I to location O.

While path 301 is described as transitioning in a CCW fashion, from theouter region to the inner region and back, the embodiments describedherein are not so limited. For example, in some implementations, thebeam can utilize a path that follows a clockwise (CW) rotation startingat the inner region, transitioning to the outer region and then back tothe inner region (one cycle). Path 301 can complete an entire cycle oronly a portion of a cycle, for example, involving a transition from theinner region to the outer region or the reverse.

FIGS. 3B and 3C are schematic views depicting examples of differentpaths taken with different beam cross-sectional profiles. In FIG. 3B, anelliptical (e.g., oval) beam profile 342 having a greater X dimensionthan Y dimension follows a path 341 sized such that the beamcross-sectional profiles of adjacent orbits touch but do not overlapwhen aligned along a central X axis. With constant spacing betweenorbits the beam will leave gaps, as is most evident when aligned alongthe Y axis. To cover the entire area with a minimal level of exposure,the overall path would need to be made elliptical with an aspect ratiosimilar to profile 342 with a smaller total Y dimension than Xdimension. FIG. 3C shows an example with circular cross-sectionalprofile 352 taking a path 351. While no gaps exist in FIG. 3C, theamount of orbits is greater (just over 4, as compared with 3.75 for FIG.3B).

FIGS. 4A-4B are schematic views depicting an example embodiment of ascanning (or raster) profile 400 formed by a cycle 405 scanned multipletimes at different radial orientations to form a group of radiallyshifted instances of the cycle. In this embodiment each instance ofcycle 405 has the same pattern and a stopping location that differs fromthat instance of cycle 405's starting location. FIG. 4A depicts a cycle405 formed by a beam path 406 where starting position A and stoppingposition O are in different locations that, in this example, are offsetby 180 degrees. Cycle 405 is rotatable or clockable for repetition atdifferent radial orientations to form a closed loop.

Scanning profile 400 is depicted in FIG. 4B. Here, scanning profile 400includes two instances of cycle 405 with a difference of 180 degrees inradial orientation between them. The first instance of cycle 405 isshown by path 401, which is depicted with starting location A1, midpointI1, and stopping location O1 in the same positions as in FIG. 4A. Thesecond instance of cycle 405 is shown by path 402, which has startinglocation A2, midpoint I2, and stopping location O2. Path 402 has thesame shape as path 401 but has been rotated (or clocked) by 180 degrees.For example, clocking forward can be implemented by evenly advancing thetransformed theta coordinate over the A1 to O1 cycle, such that O1 ends180 degrees off A1. Every location on path 401 is radially offset fromthat same or corresponding position on the next path 402 in the sequenceby the same radial amount. Each of locations A2, I2, and O2 are shown inpositions 180 degrees from A1, I1, and O1, respectively. In this and theother embodiments described herein, the clocking of cycles can beperformed in a CW or CCW direction.

The stopping location of a first cycle (e.g., O1) is at or adjacent tothe starting location of the immediately subsequent shifted cycle (e.g.,A2), such that the beam can move in uninterrupted fashion from instanceof cycle 405 to the next. The starting location A1 of the first cycle(e.g., path 401) and the stopping location O2 of the last cycle of thegroup (e.g., path 402) is substantially the same or adjacent to eachother. Thus, the profile formed by the group of two or more radiallyshifted cycles has the same (or adjacent) starting and stoppinglocations, and forms a closed loop. A group of two or more cycles eachhaving the same pattern, where each cycle has a starting location and astopping location at the same distance (or radius) from a central point,and each cycle is rotatable in orientation such that adjacent cycles canbe concatenated together to form a closed loop for the group, isreferred to herein as a super cycle. Scanning the target 196 can involvemoving the beam through a first cycle at a first radial orientation(e.g., path 401), then moving the beam through the same cycle at leastone more time (e.g., path 402) but with the subsequent cycle at a radialorientation different from that of the first cycle. This process repeatsuntil the super cycle is completed, at which time the process ofscanning repeats itself. The scanning process can be continuouslyrepeated until the overall procedure, e.g., the BNCT treatment, iscomplete.

The terms radial orientation, radial shift, and radial offset are usedherein to describe a cycle that, as a whole, can be rotated (or clocked)about a central point without changing the cycle's fundamental shape.For example, in FIG. 4A, cycle 405 has a first radial orientationindicated by path 401. Cycle 405 is then radially (circumferentially)shifted by 180 degrees to the second radial orientation indicated bypath 402. The radial offset between the two instances 401, 402 of cycle405 is 180 degrees. The characterization can be similarly expressed bysubstituting the term azimuthal for radial (e.g., azimuthal orientation,azimuthal shift, and azimuthal offset). For example, a value of thetacan define a position of an azimuth about a central point on thescannable surface (similar the hour hand of a clock, where an azimuth ata three o'clock position corresponds to a theta of 90 degrees, at sixo'clock is a theta of 180 degrees, at nine o'clock is a theta of 270degrees, etc.), and positions of cycles can be expressed with referenceto theta and the azimuth.

FIGS. 4C and 4D are schematic views depicting a cycle 415 that isrepeated four times with a difference of 90 degrees in radialorientation between adjacent instances to form another example ofscanning profile 400. In FIG. 4C, cycle 415 is formed by a beam path 411which starts at location A1 and proceeds in CCW fashion to midpoint I1in the inner region of surface 210, and then back to the outer region atstopping location O1. Stopping location O1 is radially offset CCW fromstarting location A1 by 90 degrees, which is the same amount of radialoffset that is present between the cycles 415 of this profile 400. FIG.4D depicts a second instance of cycle 415 indicated by path 412 havingstarting location A2, midpoint I2, and stopping location O2. FIG. 4E isthe same as FIG. 4D but with a third instance of cycle 415 added asindicated by path 413 having starting location A3, midpoint 13, andstopping location O3. FIG. 4F is the same as FIG. 4E but with a fourthinstance of cycle 415 added as indicated by path 414 having startinglocation A4, midpoint 14, and stopping location O4, to form thecompleted super cycle of scanning profile 400. When this embodiment ofscanning profile 400 is used, the beam is transitioned through path 411,then path 412, then path 413, and then path 414 to complete the supercycle, and this super cycle can then be repeated continuously throughoutthe entire procedure.

In the example illustrated by FIG. 4G, the scanning profile 400 is asuper cycle including three instances 421, 422, 423 of the same cyclebut with a difference of 120 degrees in radial orientation betweenadjacent ones. The cycle of FIG. 4G is modified from that of FIG. 4A topermit three iterations with one closed loop. The second instance 422 isradially shifted CCW by 120 degrees from first instance 421, and thirdinstance 423 is radially shifted CCW by 120 degrees from instance 422(radially shifted CCW by 240 degrees from instance 421). Each oflocations A2, I2, and O2 are shown in positions 120 degrees CCW from A1,I1, and O1, respectively, and each of locations A3, 13, and O3 are shownin positions 120 degrees CCW from A2, I2, and 05, respectively. The beamis transitioned through instance 421, then instance 422, and theninstance 423 to complete the super cycle. The super cycle can berepeated continuously multiple times throughout the entire procedure.

Additional example embodiments of scanning profile 400 can also beimplemented. The amount of radial offset between the repeated patterns301 can be determined by dividing 360 degrees by the number of patterninstances. For example, a profile 400 having five instances of a cyclecan have a radial offset of 72 degrees between adjacent cycles, aprofile 400 having six instances of a cycle can have a radial offset of60 degrees between adjacent cycles, a profile 400 having seven instancesof a cycle can have a radial offset of approximately 51.4 degreesbetween adjacent cycles, a profile 400 having eight instances of a cyclecan have a radial offset of 45 degrees between adjacent cycles, aprofile 400 having nine instances of a cycle can have a radial offset of40 degrees between adjacent cycles, a profile 400 having 10 instances ofa cycle can have a radial offset of 36 degrees between adjacent cycles,a profile 400 having eleven instances of a cycle can have a radialoffset of approximately 32.7 degrees between adjacent cycles, a profile400 having twelve instances of a cycle can have a radial offset of 30degrees between adjacent cycles, and so forth.

In some implementations the stopping location of a first instance of thecycle may not be the same as, or even close to, the starting location ofthe next instance of the cycle. For example, the beam can bridge the gapin a relatively rapid fashion that has negligible effect on the overallthermal performance and particle loading. If the beam is pulsed, theradial shift can occur in between pulses while the beam is off.

While the embodiments described herein are shown with the same cyclerepeated multiple times within a super cycle, it is noted that the cyclepattern need not be identical and differ only in radial orientation. Inpractice small variations will inherently be present given margins oferror within the system and variances of operating conditions during theprocedure. Indeed the scope of the present subject matter coversembodiments where the repeated cycle patterns are not identical, but arerather substantially the same with differences engendered by margins oferror, operating condition variances, and even programmed or otherwiseintended non-identicalities in the patterns.

In general, the thermal impact of a beam on the target can beinvestigated computationally using a computational model. Computationalmodelling can allow for selection of beam raster profiles that improveuniformity of particle loading on a target and/or can allow selection ofraster profile that reduces (e.g., minimizes) peak transient temperatureof the target. The raster profile can be characterized by a beam pathand a beam profile (e.g., circular or elliptical beam with a particulardimension), as described with reference to FIGS. 8 and 9 . In someimplementations, the raster profile can define a beam scanning velocity.

The computational model can allow investigation of the effect on atarget of varying one or more of several beam parameters, such as thebeam's size and shape. Furthermore, the beam's thermal impact can beevaluated by calculating one or more figures of merit (e.g., peaktemperature, temperature change, average temperature) and applying anumerical analysis to the figure of merit can allow the computationalmodel to be used to optimize the beam's raster profile.

Generally, the computational model can involve generating a meshed spaceencompassing the target. The computational model is illustrated in FIGS.5A and 5B, which illustrate a mesh composed of a three-dimensional gridin which the thermal effects of target 196 can be modeled. The thermaleffects are modeled by solving a one-dimensional heat transport equationat each “pixel” (e.g., each x-y square of the grid shown in 5A). Theone-dimensional heat transport equation (u_(t)=c²u_(xx), defining thetemperature in a pixel using the constant c as the thermal diffusivity)is solved for thermal transport through the depth of the pixel, in Zdirection, as shown in 5B. Cross talk between pixels or lateral heatconduction between pixels is assumed to be negligible, such that heatonly moves horizontally in Z direction, allowing the 1D approach to beused. It is assumed that the pixels do not include internal heat sourcesor sinks. Compositional changes are accounted for through the depth ofthe pixel. Any suitable computational approach to solving theone-dimensional heat transport differential equation can be used. Forexample, numerical approaches can include finite-element andfinite-difference approaches. For either of the finite-element andfinite-difference techniques, the target 196 can be represented in aplan view 220 as a portion of a grid 226 (as illustrated in FIG. 5A).The size of the grid can vary and can be selected based on the size ofthe target, the beam size, and the desired computational efficiency andresult accuracy. Generally, a smaller size can give more accurateanswers but at computational cost. In the current example shown in FIG.5A, the grid 226 includes 36×36 pixels (cells), but generally, thenumber of pixels can be within the range 103-105 or more. The grid canbe divided to include at least two regions: exclusion regions andregions of interest. The exclusion regions can be avoided using pathavoidance by programmed waveform (e.g., path avoidance 258 describedwith reference to FIG. 2D) or the scan within the exclusion regions canbe minimized using velocity changes (e.g., maximizing velocity withinthe exclusion regions to decrease the scanning duration and thereby theflux of the particle beam). Generally, the grid can have the same unitcell size in each dimension or the size in each dimension can differ.Resolution can be selected to provide the ability to model beams ofdifferent size and structure in line to the physical capabilities of thesystem under study.

FIG. 5B is an example of a model of a target side view 530 of the target196 illustrated in FIG. 5A. The model of the target side view 220includes multiple layers that can correspond to the layers 201, 202, 203described with reference to FIGS. 1 and 2 . In some implementations, thelayers can have a thickness defined by the pixels of the numerical grid226. In some implementations, a boundary of the target layer 201 ismodeled as corresponding to vacuum and a boundary of the targetsubstrate 203 is modeled as corresponding to a coolant fluid (e.g.water) including cooling lines 130, defining the boundary conditions ofthe one-dimensional heat transport equation.

FIGS. 6A-6D show examples of simulated thermal maps using the modeldescribed with reference to FIGS. 5A and 5B. FIGS. 6A and 6B showexamples of simulated thermal maps 610, 620 determined using thecomputational model as described above for 10 mm and 20 mm beam sizes,respectively. FIGS. 6C and 6D show examples of simulated thermal maps630, 640 determined using an ANSYS® engineering simulation software for10 mm and 20 mm beam sizes, respectively. The model used to generate thesimulated thermal maps 610, 620 is based on a transient code that tracksthe surface particle loading based on any given beam profile incombination with any raster profile. The model was benchmarked against atransient model calculated with a three-dimensional heat transfer codeANSYS® as validation.

The overall profile of the simulated thermal maps 610, 620, 630, 640calculated based on assumption of a scanning frequency of 120 Hzgenerally matches for both 10 mm and 20 mm beam sizes. For example,FIGS. 6A and 6C both show a surface temperature distribution with adistinctive heat maximum corresponding to the center of the 10 mm protonbeam. The highest average lithium surface temperature was 284° C. asdetermined by the model and 299° C. as determined by the ANSYS® model.The temperature drop from the center of the 10 mm proton beam to themargins of the 10 mm proton beam registered 162.7° C. as determined bythe model and 177.7° C. as determined by the ANSYS® model. FIGS. 6B and6E both show a dispersed surface temperature distribution correspondingto the 20 mm proton beam. The highest average lithium surfacetemperature was 177° C. as determined by the model and 184° C. asdetermined by the ANSYS® model. The temperature drop from the center ofthe 20 mm proton beam to the margins of the 20 mm proton beam registered55.7° C. as determined by the model and 63.3° C. as determined by theANSYS® model The fact that some of the calculated temperature values areabove the acceptance limit for Lithium shall not undermine the validityof the model.

Table 1 shows heating map simulation results that enable a comparisonbetween the predicted temperature variation (ΔT) and peak temperature(T_(max)) as determined using the model described with reference toFIGS. 5A and 5B and using an ANSYS® engineering simulation software. Thedata was generally analyzed to determine the correlation between themodeled values with respect to the values determined using thecomputationally expensive ANSYS® engineering simulation software todetermine the reliability of the developed model. The reliability of themodel is reflected by the differences in the thermal results. Atemperature rise difference of about 10% was found between the two setsof results, indicating agreement between the model and the transientANSYS® model.

TABLE 1 Model ANSYS % Diff Model ANSYS (10 mm) (10 mm) (10 mm) (20 mm)(20 mm) % Diff ΔT 162.7° C. 177.7° C. 8.44% 55.7° C.  63.3° C. 12.01%T_(max)   284° C.   299° C. 5.02%  177° C. 184.6° C.  4.11%

As is evident from the raster patterns shown in FIGS. 3A-5G, there arenumerous points in each pattern where the beam path crosses itself. Eachcrossing point is a location where the target surface is exposed to asignificantly higher particle flux (e.g., double) than locations wherethe target surface is exposed just a single time for each super cycle.Where the time between consecutive passes over a crossing point isrelatively long, and heat from the first pass can be sufficientlydissipated before the second exposure, the increased dose associatedwith the second exposure may not result in excessive heating at thecrossing point. However, where a crossing point is exposed twice in arelatively short period, these crossing points can be locations ofunacceptably high thermal loads. Accordingly, in some implementations,the computational models described above can be used to reduce thermalload on a target by determining paths that reduce the number of crossingpoints that experience multiple passes of the beam in quick succession.

For example, a computational model can be used to vary parameters of araster profile to avoid crossing the beam path recently traversed withina threshold time period below which excessive heating of that targetlocation may occur. FIGS. 7A-7D are schematic views depicting examplesof raster patterns that are instructive in demonstrating such recentpath avoidance (RPA) strategies. In some implementations, the RPApattern can be determined based on an iterative process. The iterativeprocess can start with a trochoid shape, defined as an (x(t), y(t))position for a given time (t). For radii, r₁, r₂ and frequencies ω₁, ω₂,the basic trochoid follows the following equations over time t:

x(t)=r ₁ cos(ω₁ ·t)+r ₂ cos(ω₂ ·t)

y(t)=r ₁ sin(ω₁ ·t)+r ₂ sin(ω₂ ·t).

For an L-lobed trochoid with outer radius, r_(max), and inner radius,r_(min), the values for the radii and frequencies are:

r ₁=−(r _(max) +r _(min))/2

r2=(r _(max) −r _(min))/2

ω₁ =L+1

ω₂=1

A radius with a maximum radius value r_(max) substantially equal to thebeam width and a minimum radius value r_(min) substantially equal tohalf the beam width can provide good results for a uniform-intensitybeam. Optimal values for r_(max) and r_(min) can be found throughoptimization algorithms and a heat simulation code.

Setting t to be time dictates the speed at which the raster moves, whichcan be varied based on capabilities of the steering magnets and a targetburning risk. For example, a high raster speed may exceed the capabilityof the steering magnets or a low raster speed may lead to burning of thetarget (if exposed too long to a particular radiation dose). For allmodified trochoid raster profiles, the next beam position is calculatedsuch that the velocity remains approximately constant. Varying thevelocity based on the beam position may offer another route forimprovement. The optimal velocity profile can be found by training amachine-learning algorithm on the results generated by the heatsimulation code, as described with reference to FIGS. 9A and 9B.

A constant-velocity trochoid pattern can give good results in targetusage but could lead to overheating. For example, the trochoid patternvisits the center of the target with a fairly high frequency because asthe trochoid path continuously follows each lobe. In order to solve theheating problem, the raster pattern can be modified such that instead offollowing the path along each lobe continuously, the ω=(L−1)^(th) lobeorder is used. Visiting the lobes in this order gives the centeradditional time to cool down between lobes. This is where the nameRecent Path Avoidance (RPA) raster comes from, as recently visited pathsare avoided, prolonging the time it takes for the beam to cross itsrecent path. For some values of L, it may be optimal to take lobes morefrequently than every ω=(L−1)^(th) lobe. Any lobe frequency, ω that iscoprime with the total number of lobes, L, could work depending on thephysical parameters of the system (beam profile, target shape, targetmaterial, etc.). The choice of lobe frequency co can be optimizedthrough computational techniques, such as using a machine learningalgorithm.

In some implementations, the raster path includes a modification of r₁and r₂ to create a filter that only allows the raster path to followevery (L−1)^(th) lobe and otherwise to follow the r_(max) value to allowthe center of the target time to cool down.

For example, an initial RPA raster (RPA One) can include the followingradii and frequencies:

${r_{1} = {{- \left( {r_{\max} + r_{\min}} \right)} \cdot {\cos\left( {\frac{L}{2 \cdot \left( {L - 1} \right)} \cdot t} \right)}^{E}}}{r_{2} = r_{\max}}{\omega_{1} = {L + 1}}{\omega_{2} = 1}$

The exponent E can be greater than 10 and smaller than 1000 (10<E<1000).The exact value of the exponent E can depend on multiple factors. Forexample, E can be set to be large enough to give a well-defined windowfor the filter to avoid having the raster oscillate around theperimeter, which may cause the beam to miss the target. E has to be setsmaller than a threshold value that defines a very small window thatwould cause the lobes to become too narrow, overheating the target. Insome implementations, E can be set such that E=100 (L−3) with L beinggreater than or equal to 4 and smaller than or equal to 8 (4≤L≤8).

RPA-One works well for minimizing heating, but can leave a region of thetarget, such as an exclusion zone, underutilized. RPA-One can be used todevelop RPA-Two, which adds another term to r₁, to define another set ofL lobes that can fill in the underused region. RPA Two uses thefollowing radii and frequencies:

${r_{1} = {{{- \left( {r_{\max} + r_{\min}} \right)}{\cos\left( \frac{L \cdot t}{{2L} - 1} \right)}^{E}} - {r \cdot {\cos\left( \frac{L \cdot t}{2 \cdot \left( {{2L} - 1} \right)} \right)}^{E}}}}{r_{2} = r_{\max}}{\omega_{1} = {{2L} + 1}}{\omega_{2} = 1}$

The coefficient r can be greater than r_(min) and smaller than thedifference between the radii limits r_(max) and renin(r_(min)<r<r_(max)−r_(min)). The exponent E can be greater than 100 andsmaller than 10000. The exact values of the coefficient r and exponent Ecan be optimized using the heat simulation and an optimizationalgorithm. In some implementations, one or more additional rasters(RPA-N) can be determined by adding terms to r₁, each new term can beoptimized to minimize target heating and target usage variation.

FIG. 7A illustrates an example of a modified raster pattern 710, whereinthe order of the lobes 702, 706, 704 is modified to extend the coolingperiod of the points where the beam path crosses itself, generating arecent path avoidance (RPA) pattern. The time duration betweensubsequent beam crossing points is directly proportional to the arclength traversed by the beam between respective consecutive crossings.For example, considering the startup point 705 of the modified rasterpattern 710, the first crossing point is 705 g, which is associated witha longer arc length than the arc length corresponding to the firstcrossing point 705 a of the trochoid raster pattern 700.

In some implementations, the RPA pattern can be further modified, as themodified raster pattern 710, to fill underused regions of the targetwithin the regions of interests and to preferentially load quadrantsthat are outside the exclusion zones. The modified raster pattern 710can be combined with the variable velocity technique to minimize loadingin the exclusion zones.

FIGS. 7B and 7C are schematic views depicting examples of recent pathavoidance (RPA) patterns 720 that are repeated multiple (e.g., four)times to form a full super cycle of the scanning profile. FIG. 7Billustrates the first cycle 722 of the RPA pattern. The first cycle 722of the RPA pattern 720, starting at 722A and stopping at 7220, includesmultiple beam crossing points 725 a, 725 b, 725 c, 725 d where the beampath crosses itself. For example, considering the startup point 722A ofthe first cycle 722 of the RPA pattern 720, the first beam crossingpoint is 725 a, the second beam crossing point is 725 b, the third beamcrossing point is 725 c, and the fourth crossing point is 725 d.

FIG. 7C illustrates the second cycle 724 of the RPA pattern 720 that canbe performed after the completion of the first cycle of the RPA pattern.The second cycle 724 of the RPA pattern 720, starting at 724A andstopping at 7240, includes multiple beam crossing points 735 a, 735 b,735 c, 735 d where the beam path crosses itself. For example,considering the startup point 724A of the second cycle 724 of the RPApattern 720, the first beam crossing point is 735 a, the second beamcrossing point is 735 b, the third beam crossing point is 735 c, and thefourth crossing point is 735 d. Each cycle of the RPA pattern 720includes a stopping position 7220, 7240 distanced from a startingposition of the corresponding cycle 722A, 724A. The stopping position ofa cycle (e.g., stopping position 7220 of the first cycle) corresponds tothe starting position of the subsequent cycle (e.g., starting position724A of the second cycle).

FIG. 7D illustrates an example of a trochoid raster pattern 726 that canbe generated by directing the beam towards a (static or rotating)target. The trochoid raster pattern 726 can be used as an initial rasterpattern for an iterative process, as described with reference to FIG. 10. The trochoid raster pattern 700 can include multiple lobes 702, 704,706, 708 (e.g., 4 four lobes as illustrated in FIG. 7A). The velocity ofthe particle beam can be varied from one lobe to another, such that thevelocity is maximized for a lobe (e.g., lobe 704) that is within anexclusion zone 254 of the target to minimize the net deposited energywithin the an exclusion zone 254, such that the target generates arelatively lower neutron flux in the exclusion zone 254 than in theregion of interest of the target. The trochoid raster pattern 700includes multiple beam crossing points 705 a, 705 b, 705 c, 705 d, 705e, 705 f, 705 g, 705 h, 705 i, 705 j, 705 k, 7051, 705 m, 705 n wherethe beam path crosses itself. For example, considering the startup point705 of the trochoid raster pattern 700, the first beam crossing point is705 a, the second beam crossing point is 705 b, the third beam crossingpoint is 705 c, the fourth crossing point is 705 d, and the fifthcrossing point is 705 e.

FIG. 8 shows examples of neutron flux radial distribution based ondifferent proton beam raster patterns from a neutron targetcorresponding to target scanning using the RPA pattern described withreference to FIGS. 7A-7C. The examples of neutron flux radialdistribution 802, 804, 806, 808, 810, 812 indicate the neutron fluxrelative to different regions of the target, including exclusion areas254 and regions of interest 256, defined relative to the radius of thetarget. A traditional neutron flux radial distribution 802 presents aGaussian distribution that is independent from the exclusion areas 254and the regions of interest 256. Some neutron flux radial distributions804, 808, 810 present a minimal distribution within the exclusion areas254 and a maximum distribution within the regions of interest 256. Anexample of a neutron flux radial distribution 806 presents a maximumdistribution within the exclusion areas 254 and a minimal distributionwithin the regions of interest 256. A volume neutron flux radialdistribution 812 presents a step distribution that is independent fromthe exclusion areas 254 and the regions of interest 256.

FIGS. 9A-9M show examples of simulation results for multiple beamprofiles to compare target usage and (fast and epithermal) neutron fluxspatial distribution at the edge of the water lines (e.g., 1-10 cm) fromthe target surface. Simulations 802 and 804 use variations on the innerdiameter of raster pattern 300. Simulations 806, 808, and 810 arevariations of raster patterns shown in FIG. 7D. 812 is a curve thatcorresponds to a uniform proton beam across the face of the target, i.e.no raster.to highlight variation caused by the different beam profiles.FIG. 9A shows the simulated usage map 902 for a traditional step beam.FIG. 9C shows the simulated usage map 908 for a 10 mm circular beamhaving a frequency of 120 Hz that is adjusted to have a minimum flux inthe exclusion areas. FIG. 9G shows the simulated usage map 914 for a 10mm circular scan inner radius having a frequency of 120 Hz. FIG. 9Jshows the simulated usage map 920 for a 15 mm circular inner scan radiushaving a frequency of 120 Hz. FIG. 9M shows the simulated usage map 926for a 20 mm circular inner scan radius having a frequency of 120 Hzadjusted to have a minimum flux in the exclusion areas, as illustratedin FIG. 8 .

FIGS. 9B, 9C, 9E, 9F, 9H, 9I, 9K, 9L, 9N, 9O show neutron simulations ofneutron flux spatial distribution at 4 cm (at the edge of the waterlines) from the target surface for different raster patterns thatproduced the target performance (usage) shown in FIGS. 9A, 9D, 9G, 9J,9M. Two metrics of interest that can define the effectiveness of theraster pattern include the neutron energy and the beam uniformity. Theneutron energy can be divided into three different energy groups:thermal (E<E₁, for example, 1 eV-100 eV), epithermal (E₁<E<E₂), as shownin FIGS. 9C, 9F, 9I, 9L, 9O, and fast (E>E₂, for example, 30 keV-50keV), as shown in FIGS. 9B, 9E, 9H, 9K, 9N. The significance of theassigned neutron energy groups is not arbitrary. During a normaltreatment cycle the patient can receive an unhealthy dose that exceedsthat of the beneficial dose if the neutron beam is too fast or toothermal. The optimal neutron energy range, for patient treatment, iswithin the epithermal range.

The ideal beam for treatment is planar—meaning a patient can be treatedwith a neutron beam that is spatially uniform over a large surface areasuch that the beam is of similar intensity and energy at the center asit is on the edges, as illustrated in FIGS. 9F, 9O. The neutron energyand the beam uniformity can vary with the raster pattern and withcooling lines or other obstacles that are between the target and thepatient, shown in FIGS. 9B, 9C, 9E, 9F, 9H, 9I, 9K, 9L, 9N, 9O, as aperturbation from the water line that occurs at a 45-degree angle(reference FIG. 2D).

The fast neutron spatial distribution intensity plots (FIGS. 9B, 9R, 9H,9K, 9N) illustrate that the intensity of the fast flux is visiblyreduced and the intensity approaches round as the proton beam isminimized in the exclusion areas. Similarly, the epithermal neutronspatial distribution intensity plots (FIGS. 9C, 9F, 9I, 9L, 9O) showthat epithermal flux increases within the center portion of the targetand a higher level of roundness is observed as the proton beam isdecreased in the exclusion areas (e.g., the center section of thetarget). While none of these patterns have been specifically optimizedfor the neutron yield, the neutron spatial distribution intensity plotsshow that avoiding regions of highly attenuating material isadvantageous for producing a more desirable treatment beam.

FIG. 10 is a flowchart depicting an example process 1000 that can beexecuted in accordance with implementations of the present disclosure. Avariety of possible raster profiles for scanning a proton beam across atarget including an exclusion area and a region of interest. The rasterprofiles can be generated using a computer processing system (1002).Each raster profile defines a different scanning pattern of a targetthat can be configured to avoid the exclusion areas of the target, asdescribed with reference to FIG. 7A or other scanning patterns describedabove. The scanning pattern can be characterized by one or more pathparameters. In some implementations, the parameters include one or moreof the following parameters: a net deposited energy, a beam intensity,an angular frequency associated with each lobe of the path of the protonbeam, a linear velocity of the proton beam across a surface of thetarget, a number of radial scan layers in a super cycle of the path ofthe proton beam, a traversal order of the lobes, and a number of supercycles of the path of the proton beam. The angular frequency and theangular velocity of the proton beam can vary for different lobes of theRPA pattern, for example to minimize the proton beam flux and the netdeposited energy within exclusion areas by completely avoiding theexclusion areas or by minimizing the time the particle beam is scanningthe exclusion areas. The velocity of a scan profile can the transformedto accelerate the velocity near an exclusion area as depicted in FIGS.2D and 8 . For example, a relative velocity function can be introduced:

Vt(q)=Vn(q)*(1+c*f(q)),

where c is the velocity accelerator and f(q) is local switch on functionsuch as a Gaussian

f(q)=exp(−((q−q_(ko))²/(2s²) such that q_(ko) is the keep out angle ands is the keep out width. The angle can be varied to avoid scanning ofexclusion regions, such as region 254 discussed with reference to FIG.2D. The f(q) function can be generalized in both planer coordinates toenable exclusion of multiple regions of different geometries and sizes.

The traversal order of the lobes can be a forward order, a reverse orderor a coprime order. The path parameters characterize the path of theproton beam across the target. The path parameters of the selectedraster profile define a path for the proton beam having a minimum delay(exceeding a threshold period) between successive exposures of a singlelocation of the target to the proton beam to minimize target damaging.In some implementations, the possible raster profiles include a maskthat can be formed based on real time measurements based on imaging data(e.g., thermal maps of the target). The mask can define a scan profileconfigured to avoid weak areas (e.g., areas heated near to the meltingpoint) or damaged regions of the scannable area.

In addition to a scanning pattern, each of the raster profiles includessettings for one or more beam parameters. Each of the beam parameterscharacterizes a property of the proton beam. The beam parameters caninclude one or more of the following parameters: a beam dimension (e.g.,a diameter of a circular beam), a beam shape, and a beam structure. Insome implementations, the beam dimension is in a range from 10 mm to 30mm. Raster profiles can be modified with a normalization coefficient inthe X and Y direction depending to the beam shape. The beam shape can becircular or elliptical. If the beam shape is elliptical, the scan can bemodified to change effectively by lowering the scan radius in thedirection that the beam is the largest so that the beam does not scanoutside the outer boundary of the region of interest. The structure ofthe beam refers to the beam flux or intensity distribution across itscross section. In some implementations, the distribution can besubstantially constant or Gaussian. In certain implementations, thedistribution can have more than one peak, such as for an annular beamstructure.

One or more target parameters characterizing the target are alsoestablished using the computer processing system (1004). For example,the target parameters can include of: target surface area, targetthickness, and/or target composition.

Neutron flux spatial distribution at 4 cm (at the edge of the waterlines) behind the target surface can be calculated for each of thepossible beam raster profiles or at a general distance (1006).Generally, the neutron flux spatial distribution is based on a thermalloading of the target by the proton beam for the corresponding possibleraster profile, target usage, and location of one or more perturbationsources (e.g., cooling lines). In some implementations, calculating theneutron flux spatial distribution includes, for each of the possibleraster profiles, calculating a thermal load at each of a plurality ofdiscrete portions of the target based on a linear relationship betweenthe thermal load and a proton flux at each discrete portion for thecorresponding raster profile. In some implementations, each discreteportion corresponds to an area of a surface of the target in the path ofthe proton beam that is smaller than a dimension of the proton beam. Insome implementations, the thermal load at each discrete portion iscalculated based on heat transfer through a depth of the target awayfrom a surface of the target on which the proton beam is incident. Insome implementations, the neutron flux spatial distribution is selectedbased on the neutron energy and the beam uniformity. The neutron energycan selected from three different energy groups: thermal (E<E₁),epithermal (E₁<E<E₂), and fast (E>E₂) The optimal neutron energy forpatient treatment has a range within the epithermal category, has aspatially uniform distribution over a large surface area such that thebeam is of similar intensity and energy at the center as it is on theedges.

A raster profile is selected from among the possible raster profilesbased on the value of the figure of merit and based on the measuredproperty of the target (1008). In some implementations, the selection ofthe raster profile includes a presentation of an operator of the protonbeam with a list of the possible raster profiles and receiving, via auser interface of the computer system, a user input including aselection from the list by the operator. In some cases, raster profileselection can occur automatically, e.g., based on measurements of eitherthe beam properties, target properties, or both. For instance, where athreshold level of heating is detected on the target, the system canswitch to a different raster profile that puts less stress on thelocation where the threshold load is detected. In some implementations,the system uses an active feedback or feedforward process andperiodically adjusts the raster profile to prolong the useful life ofthe target.

In some implementations, multiple raster profiles can be selected ascandidate profiles, F_(k)(t), and cutover functions, s_(k)(t), can beapplied to switch between profiles. The output profile, F (t), can bedefined by:

F(t)=Σ_(k=1) ^(n) s _(k)(t)F _(k)(t)

where Σ_(k=1) ^(n)s_(k)(t)=1 for every value tin the domain of theoutput profile.

For example, a simple linear crossover between two profiles, F1(t) andF2(t), starting at t1 and ending at t2 could be described by definings1(t) and s2(t) as follows:

${s_{1}(t)} = \left\{ {{\begin{matrix}1 & {t < t_{1}} \\{1 - \frac{t - t_{1}}{t_{2} - t_{1}}} & {t_{1} \leq t \leq t_{2}} \\0 & {t > t_{2}}\end{matrix}{s_{2}(t)}} = \left\{ \begin{matrix}0 & {t < t_{1}} \\{0 + \frac{t - t_{1}}{t_{2} - t_{1}}} & {t_{1} \leq t \leq t_{2}} \\1 & {t > t_{2}}\end{matrix} \right.} \right.$

After selection of a particular raster profile, the proton beam isscanned across the target according to the selected raster profile(1010).

One or more properties of the beam are measured (1012) as part ofprocess 1000. In some implementations, the properties of the beam aremeasured upstream from the target. The beam properties that can bemeasured include, for example, a beam size, a beam structure, and a beamprofile, as described with reference to FIGS. 9A-9O. The beam profilecan be measured using infrared cameras configured to determine the beamshape at the target location. A neutron yield measurement of the BNCTsystem can be included as part of the active feedback controller. Sincethe raster pattern effects the neutron output this can be a measurablequantity that provides an active feedback.

One or more properties of the target are measured (1014) as part ofprocess 1000. In some implementations, the one or more properties of thetarget include a temperature of the target at one or more locationsacross the target relative to perturbation sources (e.g., coolinglines). For example, one or more thermal sensors (e.g., infraredcameras) can detect the temperature of the target at a correspondinglocation within a region of interest. In some implementations, atemperature map of the target can be acquired by a thermal camera. Themeasured temperature can be used as an input to dynamically adjust orchange the raster profile during the scanning process to avoid localoverheating of the target. In some cases, the system can pause beamoperation entirely to avoid overheating the target and resume operationonce the target cools to an acceptable level.

Thus, implementations of the present disclosure can include a number ofadvantages. In some examples, the described techniques provide accurateestimations of target heating and usage with minimized computationresource requirements. Designs described herein illustrate advantages ofparticular raster profiles and beam profiles that can extend thelifetime of a target, by maintaining peak temperature under the damaging(e.g., blistering) temperature of the target. The describedimplementations can also enable an improved performance of BNCT, byproviding an even distribution of particle loading on the regions ofinterest of the target such that the target generates a relatively lowerneutron flux in the exclusion areas to compensate for the perturbationsthat can be generated by system components, which positively affects theprofile of the particle beam that irradiates the patient.

In one aspect, this document describes a method of operating a beam,including directing the particle beam along an axis so that the particlebeam is incident on a target positioned on the particle beam axis, thetarget having a scannable surface extending over an area substantiallyorthogonal to the axis, scanning the particle beam across the scannablesurface of the target along a first path, the particle beam having afirst flux while being scanned along the first path, and selectivelyscanning the particle beam across the scannable surface of the targetalong a second path, the particle beam having a second flux while beingscanned along the second path, wherein the first path forms a firstpattern at a first radial orientation with respect to the axis, and thesecond path forms substantially the first pattern at a second radialorientation with respect to the axis different from the first radialorientation, the second path being within an exclusion area of thetarget, the second flux being lower than the first flux. The particlebeam is scanned with a first velocity along the first path and a secondvelocity along the second path, the first velocity being lower than thesecond velocity. The particle beam has a first net deposited energy whenscanned along the first path that is higher than a second net depositedenergy of the particle beam along the second path. The exclusion area ofthe target corresponds to a cooling line positioned at an axial locationdownstream from the target and that overlaps the area of the scannablesurface. Selectively scanning the particle beam across the scannablesurface of the target includes excluding the second path. Selectivelyscanning the particle beam across the scannable surface of the targetresults in a neutron flux that is spatially uniform within the plane andfalls within and is optimized to an energy range for boron neutroncapture therapy treatment. The first pattern path and the second pathdefine the exclusion area of the target. The first pattern has a firsthalf and a second half, wherein the first and second halves aresymmetrical. The first pattern has a start location and a stop location,wherein the start location is at or adjacent to the stop location. Thefirst radial orientation differs from the second radial orientation by180 degrees. The method of claim 1, can further include: scanning theparticle beam across the scannable surface of the target along a thirdpath, wherein the third path forms the first pattern at a third radialorientation different from the first and second radial orientations. Thefirst, second, and third radial orientations differ by 120 degrees. Themethod can further include: scanning the particle beam across thescannable surface of the target along a fourth path, wherein the fourthpath forms the first pattern at a fourth radial orientation differentfrom the first, second, and third radial orientations. The first,second, third, and fourth radial orientations differ by 90 degrees. Themethod can further include: scanning the particle beam across thescannable surface of the target along a fifth path, wherein the fifthpath forms the first pattern at a fifth radial orientation differentfrom the first, second, third, and fourth radial orientations. Thefirst, second, third, fourth, and fifth radial orientations differ by 72degrees. The first path corresponds to a first instance of a cycle, andthe second path corresponds to a second instance of the cycle. Scanningof the first instance of the cycle and the second instance of the cycleforms a closed loop. The particle beam is a proton beam. The scannablesurface is a lithium or beryllium surface. The target generates neutronswhen scanned. The particle beam has a circular cross-sectional profile.The particle beam has an elliptical cross-sectional profile. Theparticle beam has an annular cross-sectional profile. The particle beamhas a hollow cross-sectional profile. The particle beam is generated bya beam system including: an ion source, a first beamline coupled withthe ion source, a tandem accelerator coupled with the first beamline, asecond beamline coupled with the tandem accelerator, and the targetcoupled with the second beamline. The pattern exposes a majority of thescannable surface to the particle beam. The second path forms the firstpattern at the second radial orientation different from the first radialorientation.

In another aspect, this document describes a beam system including: acomputing device including a processor communicatively coupled withmemory, wherein the memory stores a plurality of instructions that, whenexecuted by the processor, cause the processor to: control movement of aparticle beam across a scannable surface of a target along a first path,the particle beam having a first flux while being scanned along thefirst path, and control movement of the particle beam across thescannable surface of the target along a second path, the particle beamhaving a second flux while being scanned along the first path, whereinthe first path includes a first pattern at a first radial orientation,and the second path includes substantially the first pattern at a secondradial orientation different from the first radial orientation, thesecond path being within an exclusion area of the target, the secondflux being lower than the first flux. The particle beam is scanned witha first velocity along the first path and a second velocity along thesecond path, the first velocity being lower than the second velocity.The particle beam has a first net deposited energy when scanned alongthe first path that is higher than a second net deposited energy of theparticle beam along the second path. The exclusion area of the targetcorresponds to a cooling lines, diagnostics, or beam control hardwarepositioned at an axial location downstream from the target and thatoverlaps the area of the scannable surface. Controlling the movement ofthe particle beam across the scannable surface of the target includesoptimizing a scannable profile for both temperature and neutronics tominimize a peak transient temperature while spatial variations in theneutron flux are minimized and intensity of the neutron flux within thepreferred epithermal region is maximized. The first path traverses froman outer region to an inner region of the scannable surface and back tothe outer region in the first pattern. The first pattern includes aspiral and a mirror image of the spiral. The first pattern has a firsthalf and a second half, wherein the first and second halves aresymmetrical. The first path traverses from an inner region to an outerregion of the scannable surface and back to the inner region in thefirst pattern. The first pattern has a start location and a stoplocation, wherein the start location is at or adjacent to the stoplocation. The system of claim 30, wherein the first radial orientationdiffers from the second radial orientation by 180 degrees. The pluralityof instructions, when executed by the processor, further cause theprocessor to: control movement of the particle beam across the scannablesurface of the target along a third path, wherein the third pathincludes the first pattern at a third radial orientation different fromthe first and second radial orientations. The first, second, and thirdradial orientations differ by 120 degrees. The plurality ofinstructions, when executed by the processor, further cause theprocessor to: control movement of the particle beam across the scannablesurface of the target along a fourth path, wherein the fourth pathincludes the first pattern at a fourth radial orientation different fromthe first, second, and third radial orientations. The first, second,third, and fourth radial orientations differ by 90 degrees. Theplurality of instructions, when executed by the processor, further causethe processor to: control movement of the particle beam across thescannable surface of the target along a fifth path, wherein the fifthpath includes the first pattern at a fifth radial orientation differentfrom the first, second, third, and fourth radial orientations. Thefirst, second, third, fourth, and fifth radial orientations differ by 72degrees. The plurality of instructions, when executed by the processor,further cause the processor to: control movement of the particle beamacross the scannable surface of the target along a sixth path, whereinthe sixth path includes the first pattern at a sixth radial orientationdifferent from the first, second, third, fourth, and fifth radialorientations. The first, second, third, fourth, fifth, and sixth radialorientations differ by 60 degrees. The particle beam is a proton beam.The scannable surface is a surface of a lithium layer or berylliumlayer. The target generates neutrons when scanned. The particle beam hasa circular profile. The particle beam has an elliptical profile. Theparticle beam has an annular profile. The particle beam has a hollowprofile. The system is configured to perform a boron neutron capturetherapy (BNCT). The particle beam is generated by a beam systemincluding: an ion source, a first beamline coupled with the ion source,a tandem accelerator coupled with the first beamline, a second beamlinecoupled with the tandem accelerator, and the target coupled with thesecond beamline. The first pattern exposes a majority of the scannablesurface to the particle beam. The second path forms the first pattern atthe second radial orientation different from the first radialorientation.

In another aspect, this document describes a method of operating acharged particle beam in a neutron beam system, the method including:directing the charged particle beam towards a scannable surface of atarget configured to generate neutrons, and scanning the chargedparticle beam across a first volume and a second volume of the scannablesurface of the target such that the target generates a relatively lowerneutron flux in the second volume than in the first volume. The chargedparticle beam is scanned with a first velocity across the first volumeand a second velocity across the second volume, the first velocity beinglower than the second velocity. The charged particle beam has a firstenergy when scanned across the first volume that is higher than a secondenergy of the particle beam when scanned across the second volume. Thesecond volume is an exclusion zone of the target that corresponds to acooling line in a position downstream from the target between the targetand an output of the neutron beam system. The charged particle beam is aproton beam. The target includes lithium or beryllium. The chargedparticle beam is generated by a beam system including: an ion source, afirst beamline coupled with the ion source, a tandem accelerator coupledwith the first beamline, a second beamline coupled with the tandemaccelerator, and the target coupled with the second beamline.

In another aspect, this document describes a neutron beam systemincluding: a computing device including a processor communicativelycoupled with memory, wherein the memory stores a plurality ofinstructions that, when executed by the processor, cause the processorto: control movement of a charged particle beam across a scannablesurface of a target configured to generate neutrons, and controlmovement of the charged particle beam across a first volume and a secondvolume of the scannable surface of the target such that the targetgenerates a relatively lower neutron flux in the second volume than inthe first volume. The memory stores a plurality of instructions that,when executed by the processor, cause the processor to scan the chargedparticle beam with a first velocity across the first volume and a secondvelocity across the second volume, the first velocity being lower thanthe second velocity. The memory stores a plurality of instructions that,when executed by the processor, cause the processor to scan the chargedparticle beam with a first energy across the first volume and with asecond energy across the second volume, wherein the first energy isgreater than the second energy. The second volume is an exclusion zoneof the target that corresponds to a cooling line in a positiondownstream from the target between the target and an output of theneutron beam system. The charged particle beam is a proton beam. Thetarget includes lithium or beryllium. The system can further include: anion source, a first beamline coupled with the ion source, a tandemaccelerator coupled with the first beamline, a second beamline coupledwith the tandem accelerator, and the target coupled with the secondbeamline.

FIG. 11 is a block diagram showing an example system that can beimplemented in accordance with the present disclosure. For example, theillustrated example system 1100 includes a beam system 102 one or morecomputing devices 1102, and one or more servers 1110. In someimplementations, beam system 102 may be part of an example neutron beamsystem (e.g., system 102 described with reference to FIGS. 1A and 1B).The beam system 102 may employ one or more control systems 1101 withwhich one or more computing devices 1102 may communicate in order tointeract with the systems and components of the beam system 102 (e.g.,neutron beam system 102). The control system 1101 can be programmed tocontrol the steering devices (e.g., magnets, X-Y shifter) in HEBL 50that determine the X-Y position of the proton beam incident upon thescannable surface 210 of target 196. The beam system 102, the one ormore computing devices 1102, and one or more servers 1110 are configuredto communicate directly with one another or via a local network, such asnetwork 1104.

Control system 1101 can be programmed with parameters of amplitude andoffset controls that allow a fixed displacement of the beam to controllocation of the total scanned pattern. In some embodiments, theparameters are programmed in or for a digital signal processor (DSP)that controls the magnet power supply. The amplitude and offsetparameters can be input to the DSP in real time during operation, i.e.,on the fly, to correct for changes in the beam behavior or net depositedenergy to generate a uniformly distributed resultant beam thatcompensates for potential perturbations generated by system components(e.g., cooling lines). The real time parameters can form a generalizedmethod of active feedback for ion particle beam control.

Computing devices 1102 may be embodied by various user devices, systems,computing apparatuses, controllers, and the like. For example, a firstcomputing device 1102 may be a desktop computer associated with aparticular user, while another computing device 1102 may be a laptopcomputer associated with a particular user, and in yet another computingdevice 1102 may be a mobile device (e.g., a tablet or smart device).Each of the computing devices 1102 may be configured to communicate withthe beam system 102, for example through a user interface accessible viathe computing device. For example, a user may execute a desktopapplication on the computing device 1102, which is configured tocommunicate with the beam system 102.

By using a computing device 1102 to communicate with beam system 102, auser may provide operating parameters for beamline components 3005(e.g., operating voltages, and the like) according to embodimentsdescribed herein.

The control system 1101 may be configured to receive measurements,signals, or other data from components 1105 and monitoring devices 1103of the beam system 102. For example, the control system 1101 may receivesignals from one or more monitoring devices 1103 indicative of operatingconditions and/or a position of a beam passing through the beam system102. The control system 1101, depending on the operating conditionsand/or position of the beam passing through the beam system 102, mayprovide adjustments to inputs of one or more beam line components 1105according to the methods described herein. The control system 1101 mayalso provide information collected from any of the components of thebeam system 102, including the monitoring devices 1103, to the computingdevice 1102 either directly or via communications network 1104. Thecontrol system 1101 can be programmed to implement embodiments of thescanning profile as described with reference to FIGS. 4, 5 , and 7-10.

The communications network 1104 may include any wired or wirelesscommunication network including, for example, a wired or wireless localarea network (LAN), personal area network (PAN), metropolitan areanetwork (MAN), wide area network (WAN), or the like, as well as anyhardware, software and/or firmware required to implement it (such as,e.g., network routers, etc.). For example, communications network 1104may include an 802.11, 802.16, 802.20, and/or WiMax network. Thecommunications network 1104 may include a public network, such as theInternet, a private network, such as an intranet, or combinationsthereof, and may utilize a variety of networking protocols now availableor later developed including, but not limited to TCP/IP based networkingprotocols. The computing device 1102 and control system 1101 may beembodied by one or more computing systems, such as system 1200 describedwith reference to FIG. 12 .

The computing device 1102 and control system 1101 can be configured toperform operations comprising scanning the beam across a scannablesurface of a target along a first path; and scanning the beam across thescannable surface of the target along a second path, wherein the firstpath forms a first pattern at a first radial orientation, and the secondpath forms substantially the first pattern at a second radialorientation different from the first radial orientation. The beam ispulsed while scanning along the first and second paths. The beamcontinuously propagates while scanning along the first and second paths.The beam moves from an inner region to an outer region of the scannablesurface and back to the inner region in the first pattern. The beammoves from an outer region to an inner region of the scannable surfaceand back to the outer region in the first pattern. The first patterncomprises a spiral and a mirror image of the spiral. The first patternhas a first half and a second half, wherein the first and second halvesare symmetrical. The first pattern is continuously curved following acircular, parabolic, sinusoidal, or elliptic trajectory. The firstpattern has a start location and a stop location, wherein the startlocation is at or adjacent to the stop location. The first radialorientation differs from the second radial orientation by 180 degrees.The operations further comprising: scanning the beam across thescannable surface of the target along a third path, wherein the thirdpath forms the first pattern at a third radial orientation differentfrom the first and second radial orientations. The first, second, andthird radial orientations differ by 120 degrees. The operations furthercomprising: scanning the beam across the scannable surface of the targetalong a fourth path, wherein the fourth path forms the first pattern ata fourth radial orientation different from the first, second, and thirdradial orientations. The first, second, third, and fourth radialorientations differ by 90 degrees. The operations further comprising:scanning the beam across the scannable surface of the target along afifth path, wherein the fifth path forms the first pattern at a fifthradial orientation different from the first, second, third, and fourthradial orientations. The first, second, third, fourth, and fifth radialorientations differ by 72 degrees. The first path corresponds to a firstinstance of a cycle, and the second path corresponds to a secondinstance of the cycle. In some implementations, scanning of the firstinstance of the cycle and the second instance of the cycle forms aclosed loop. The beam is a proton beam. The scannable surface is alithium or beryllium surface. The target generates neutrons whenscanned. The beam has a circular cross-sectional profile. The beam hasan elliptical cross-sectional profile. The beam has an annularcross-sectional profile. The beam has a hollow cross-sectional profile.The operations performing a boron neutron capture therapy (BNCT). Thebeam is generated by a beam system comprising: an ion source; a firstbeamline coupled with the ion source; a tandem accelerator coupled withthe first beamline; a second beamline coupled with the tandemaccelerator; and the target coupled with the second beamline. Thepattern exposes a majority of the scannable surface to the beam. Thesecond path forms the first pattern at the second radial orientationdifferent from the first radial orientation.

The computing device 1102 and control system 1101 can be configured toperform operations comprising scanning the beam across a scannablesurface of a target along a first path; and scanning the beam across thescannable surface of the target along a second path, wherein the firstpath forms a first pattern at a first radial orientation, and the secondpath forms a second pattern at a second radial orientation differentfrom the first radial orientation, wherein the first and second patternsare substantially the same but for the different radial orientations.The first and second patterns are the same but for the different radialorientations.

The computing device 1102 and control system 1101 can be configured toperform operations comprising establishing, using a computer processingsystem, a plurality of possible raster profiles for scanning the protonbeam across the target, each of the plurality of possible rasterprofiles comprising one or more beam parameters, each of the one or morebeam parameters characterizing a property of the proton beam and one ormore path parameters characterizing a path of the proton beam across thetarget; establishing, using the computer processing system, one or moretarget parameters characterizing the target; calculating, using thecomputer processing system, a value of a figure of merit for each of thepossible beam raster profiles, wherein the figure of merit is based on athermal loading of the target by the proton beam for the correspondingpossible raster profile; selecting, using the computer processingsystem, a raster profile from among the plurality of plurality ofpossible raster profiles based on the value of the figure of merit; anddirecting the proton beam across the target according to the selectedraster profile. The resulting patterns are utilized in neutronicssimulations to determine the best spatially optimized and energyoptimized for the epithermal neutron range that is preferred for BNCTtreatment. As advances in BNCT occur, the recommended epithermal rangewill shift to minimize tissue damage while achieving controlled depthpenetration. Calculating the values for the figure of merit comprises,for each of the possible raster profiles, calculating a thermal load ateach of a plurality of discrete portions of the target based on a linearrelationship between the thermal load and a proton flux at each discreteportion for the corresponding raster profile. Each discrete portioncorresponds to an area of a surface of the target in the path of theproton beam that is smaller than a dimension of the proton beam. Thethermal load at each discrete portion is calculated based on heattransfer through a depth of the target away from a surface of the targeton which the proton beam is incident. The figure of merit is selectedfrom the group consisting of: a peak temperature of the target, atemperature change of the target, an average temperature of the target,and a usage efficiency of the target. The one or more beam parametersare selected from the group consisting of: a beam dimension, a beamshape, and a beam structure. The beam dimension is in a range from 10 mmto 30 mm. The beam shape is circular or elliptical. A structure of thebeam is circular or annular. The one or more path parameters is selectedfrom the group consisting of: a frequency associated with the path ofthe proton beam, a linear velocity of the proton beam across a surfaceof the target, a number of radial scan layers in a supercycle of thepath of the proton beam, and a number of supercycles of the path of theproton beam. The one or more target parameters are selected from thegroup consisting of: target surface area, target thickness, and targetcomposition. The target comprises a layer of lithium or a layer ofberyllium. The target comprises a layer of a metal supporting the layerof lithium or the layer of beryllium. Selecting comprises presenting anoperator of the proton beam with a list of the possible raster profilesand receiving, via the computer system, a selection from the list by theoperator. The operations further comprising measuring one or moreproperties of the target and selecting the raster profile based on themeasured property of the target. The one or more properties of thetarget comprise a temperature of the target at one or more locations onthe target. The operations, further comprising measuring one or moreproperties of the beam and selecting the raster profile based on themeasured property of the beam. The one or more properties of the beamare measured upstream from the target. The selected raster profiledefines a path for the proton beam having a minimum delay betweensuccessive exposures of a single location of the target to the protonbeam exceeds a threshold period. The selected raster profile defines apath based on a trochoid shape. The trochoid shape comprises a pluralityof lobes. The angular frequency of the proton beam varies for differentlobes of the trochoid shape. The selected raster profile comprises avarying angular velocity of the proton beam across the target surface.The selected raster profile comprises a varying linear velocity of theproton beam across the target surface.

The computing device 1102 and control system 1101 can be configured toperform operations comprising monitoring a temperature of a target whilescanning a proton beam across a surface of the target according to afirst raster profile; and based on the monitored temperature, changingthe scanning from the first raster profile to a second raster profile,wherein the second raster profile and the first raster profile result indiffering heating profiles of the target according to a computer modelof a thermal loading of the target by the first and second rasterprofiles. The scanning is changed in response to selection of the secondraster profile from among a plurality of raster profiles by a humanoperator of the proton beam. The scanning is changed automaticallyaccording to a feedback or feedforward algorithm. The temperature ismonitored at multiple discrete locations of the target. The temperatureis monitored by obtaining a thermal image of the target.

The computing device 1102 and control system 1101 can be configured toperform operations comprising scanning a charged particle beam across ascannable surface of a target in a super cycle, wherein the super cyclecomprises a plurality of cycles, each cycle of the plurality of cycleshaving the same shape and a different azimuthal orientation, wherein theplurality of cycles are concatenated together such that a path of thecharged particle beam traverses the plurality of cycles in a closedloop. The plurality of cycles comprises two cycles azimuthally offset by180 degrees from each other. The plurality of cycles comprises threecycles azimuthally offset by 120 degrees from each other. The pluralityof cycles comprises four cycles azimuthally offset by 90 degrees fromeach other.

Referring now to FIG. 12 , a schematic view of an example computingsystem 1200 is provided. The system 1200 can be used for the operationsdescribed in association with the implementations described herein. Forexample, the system 1200 may be included in any or all of the servercomponents discussed herein. The system 1200 includes a processor 1210,a memory 1220, a storage device 1230, and an input/output device 1240.Each of the components 1210, 1220, 1230, and 1240 are interconnectedusing a system bus 1250. The processor 1210 is capable of processinginstructions for execution within the system 1200. In oneimplementation, the processor 1210 is a single-threaded processor. Inanother implementation, the processor 1210 is a multi-threadedprocessor. The processor 1210 is capable of processing instructionsstored in the memory 1220 or on the storage device 1230 to displaygraphical information for a user interface on the input/output device1240.

The memory 1220 stores information within the system 1200. In oneimplementation, the memory 1220 is a computer-readable medium. In oneimplementation, the memory 1220 is a volatile memory unit. In anotherimplementation, the memory 1220 is a non-volatile memory unit. Thestorage device 1230 is capable of providing mass storage for the system1200. In one implementation, the storage device 1230 is acomputer-readable medium. In various different implementations, thestorage device 1230 may be a floppy disk device, a hard disk device, anoptical disk device, or a tape device. The input/output device 1240provides input/output operations for the system 1200. In oneimplementation, the input/output device 1240 includes a keyboard and/orpointing device. In another implementation, the input/output device 1240includes a display unit for displaying graphical user interfaces.

In some implementations, two components may both leverage use of thesame processor, network interface, storage medium, or the like toperform their associated functions, such that duplicate hardware is notrequired for each device. The use of the terms “device” and/or“circuitry” as used herein with respect to components of the apparatustherefore can encompass particular hardware configured with software toperform the functions associated with that particular device, asdescribed herein.

The terms “device” and/or “circuitry” should be understood broadly toinclude hardware, in some embodiments, device and/or circuitry may alsoinclude software for configuring the hardware. For example, in someembodiments, device and/or circuitry may include processing circuitry,storage media, network interfaces, input/output devices, and the like.In some implementations, other elements of the system 1200 may provideor supplement the functionality of a particular component(s).

In some embodiments, the processor 1210 (and/or co-processor or anyother processing circuitry assisting or otherwise associated with theprocessor) may be in communication with the memory 1220 via a bus forpassing information among components of the apparatus. The memory 1220may be non-transitory and may include, for example, one or more volatileand/or non-volatile memories. In other words, for example, the memory1220 may be an electronic storage device (e.g., a computer readablestorage medium). The memory 1220 may be configured to store information,data, content, applications, instructions, or the like, for enabling thesystem 1200 to carry out various functions in accordance with exampleembodiments of the present disclosure, as described with reference toFIGS. 1-11 .

The processor 1210 may be embodied in a number of different ways andmay, for example, include one or more processing devices configured toperform independently. Additionally or alternatively, the processor 1210may include one or more processors configured in tandem via a bus toenable independent execution of instructions, pipelining, and/ormultithreading. The use of the terms “processing device” and/or“processing circuitry” may be understood to include a single coreprocessor, a multi-core processor, multiple processors internal to theapparatus, and/or remote or “cloud” processors.

In some implementations, the processor 1210 may be configured to executeinstructions stored in the memory 1220 or otherwise accessible to theprocessor. Alternatively or additionally, the processor 1210 may beconfigured to execute hard-coded functionality. As such, whetherconfigured by hardware or software methods, or by a combination ofhardware with software, the processor may represent an entity (e.g.,physically embodied in circuitry) capable of performing operationsaccording to an embodiment of the present disclosure while configuredaccordingly. Alternatively, as another example, when the processor 1210is embodied as an executor of software instructions, the instructionsmay specifically configure the processor 1210 to perform the algorithmsand/or operations described herein when the instructions are executed.The instructions can include those necessary to determine a scanningprofile and scan a target, as described with reference to FIGS. 1-11 .

In some implementations, the system 1200 may include input/output device1260 that may, in turn, be in communication with processor 1210 toprovide output to the user and, in some embodiments, to receive inputfrom the user. The input/output device 1260 may include a user interfaceand may include a device display, such as a user device display, thatmay include a web user interface, a mobile application, a client device,or the like. In some embodiments, the input/output device 1260 may alsoinclude a keyboard, a mouse, a joystick, a touch screen, touch areas,soft keys, a microphone, a speaker, or other input/output mechanisms.The processor and/or user interface circuitry including the processormay be configured to control one or more functions of one or more userinterface elements through computer program instructions (e.g., softwareand/or firmware) stored on a memory accessible to the processor (e.g.,memory 1220, and/or the like).

The communications device or circuitry 1240 may be any means such as adevice or circuitry embodied in either hardware or a combination ofhardware and software that is configured to receive and/or transmit datafrom/to a network and/or any other device or circuitry in communicationwith the system 1200. The communications device or circuitry 1240 mayinclude, for example, a network interface for enabling communicationswith a wired or wireless communication network. For example, thecommunications device or circuitry 1240 may include one or more networkinterface cards, antennas, buses, switches, routers, modems, andsupporting hardware and/or software, or any other device suitable forenabling communications via a network. Additionally or alternatively,the communication interface may include the circuitry for interactingwith the antenna(s) to cause transmission of signals via the antenna(s)or to handle receipt of signals received via the antenna(s). The signalsmay be transmitted by the system 1200 using any of a number of wirelesspersonal area network (PAN) technologies, such as current and futureBluetooth standards (including Bluetooth and Bluetooth Low Energy(BLE)), infrared wireless (e.g., IrDA), FREC, ultra-wideband (UWB),induction wireless transmission, or the like. In addition, it should beunderstood that the signals may be transmitted using Wi-Fi, Near FieldCommunications (NFC), Worldwide Interoperability for Microwave Access(WiMAX), or other proximity-based communications protocols.

Any such computer program instructions and/or other type of code may beloaded onto a computer, processor, or other programmable apparatus'circuitry to produce a machine, such that the computer, processor, orother programmable circuitry that executes the code on the machinecreates the means for implementing various functions, including thosedescribed herein.

Embodiments of the present disclosure may be configured as systems,methods, mobile devices, backend network devices, and the like.Accordingly, embodiments may comprise various means including entirelyof hardware or any combination of software and hardware. Furthermore,embodiments may take the form of a computer program product on at leastone non-transitory computer-readable storage medium havingcomputer-readable program instructions (e.g., computer software)embodied in the storage medium. Any suitable computer-readable storagemedium may be utilized including non-transitory hard disks, CD-ROMs,flash memory, optical storage devices, or magnetic storage devices.

Processing circuitry in accordance with the present disclosure caninclude one or more processors, microprocessors, controllers, and/ormicrocontrollers, each of which can be a discrete chip or distributedamongst (and a portion of) a number of different chips. Processingcircuitry in accordance with the present disclosure can include adigital signal processor, which can be implemented in hardware and/orsoftware of the processing circuitry in accordance with the presentdisclosure. Processing circuitry in accordance with the presentdisclosure can be communicatively coupled with the other components ofthe figures herein. Processing circuitry in accordance with the presentdisclosure can execute software instructions stored on memory that causethe processing circuitry to take a host of different actions and controlthe other components in figures herein.

Memory in accordance with the present disclosure can be shared by one ormore of the various functional units, or can be distributed amongst twoor more of them (e.g., as separate memories present within differentchips). Memory can also be a separate chip of its own. Memory can benon-transitory, and can be volatile (e.g., RAM, etc.) and/ornon-volatile memory (e.g., ROM, flash memory, F-RAM, etc.).

Computer program instructions for carrying out operations in accordancewith the described subject matter may be written in any combination ofone or more programming languages and software platforms such as but notlimited to Python, Labview platform by National Instruments, Java,JavaScript, Smalltalk, C++, C #, Transact-SQL, XML, PHP or the like andconventional procedural programming languages, such as the “C”programming language or similar programming languages.

Various aspects of the present subject matter are set forth below, inreview of, and/or in supplementation to, the described embodiments, withthe emphasis here being on the interrelation and interchangeability ofthe following embodiments. In other words, an emphasis is on the factthat each feature of the embodiments can be combined with each and everyother feature unless explicitly stated otherwise or logicallyimplausible.

It should be noted that all features, elements, components, functions,and steps described with respect to any embodiment provided herein areintended to be freely combinable and substitutable with those from anyother embodiment. If a certain feature, element, component, function, orstep is described with respect to only one embodiment, then it should beunderstood that that feature, element, component, function, or step canbe used with every other embodiment described herein unless explicitlystated otherwise. This paragraph therefore serves as antecedent basisand written support for the introduction of claims, at any time, thatcombine features, elements, components, functions, and steps fromdifferent embodiments, or that substitute features, elements,components, functions, and steps from one embodiment with those ofanother, even if the following description does not explicitly state, ina particular instance, that such combinations or substitutions arepossible. It is explicitly acknowledged that express recitation of everypossible combination and substitution is overly burdensome, especiallygiven that the permissibility of each and every such combination andsubstitution will be readily recognized by those of ordinary skill inthe art.

To the extent the embodiments disclosed herein include or operate inassociation with memory, storage, and/or computer readable media, thenthat memory, storage, and/or computer readable media are non-transitory.Accordingly, to the extent that memory, storage, and/or computerreadable media are covered by one or more claims, then that memory,storage, and/or computer readable media is only non-transitory.

As used herein and in the appended claims, the singular forms “a,” “an,”and “the” include plural referents unless the context clearly dictatesotherwise.

While the embodiments are susceptible to various modifications andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that these embodiments are not to be limited to the particularform disclosed, but to the contrary, these embodiments are to cover allmodifications, equivalents, and alternatives falling within the spiritof the disclosure. Furthermore, any features, functions, steps, orelements of the embodiments may be recited in or added to the claims, aswell as negative limitations that define the inventive scope of theclaims by features, functions, steps, or elements that are not withinthat scope.

What is claimed is:
 1. A method of operating a particle beam, the methodcomprising: directing the particle beam along an axis so that theparticle beam is incident on a target positioned on the particle beamaxis, the target having a scannable surface extending over an areasubstantially orthogonal to the axis; scanning the particle beam acrossthe scannable surface of the target along a first path, the particlebeam having a first flux while being scanned along the first path; andselectively scanning the particle beam across the scannable surface ofthe target along a second path, the particle beam having a second fluxwhile being scanned along the second path, wherein the first path formsa first pattern at a first radial orientation with respect to the axis,and the second path forms substantially the first pattern at a secondradial orientation with respect to the axis different from the firstradial orientation, the second path being within an exclusion area ofthe target, the second flux being lower than the first flux.
 2. Themethod of claim 1, wherein the particle beam is scanned with a firstvelocity along the first path and a second velocity along the secondpath, the first velocity being lower than the second velocity.
 3. Themethod of claim 1, wherein the particle beam has a first net depositedenergy when scanned along the first path that is higher than a secondnet deposited energy of the particle beam along the second path.
 4. Themethod of claim 1, wherein the exclusion area of the target correspondsto a cooling line positioned at an axial location downstream from thetarget and that overlaps the area of the scannable surface.
 5. Themethod of claim 1, wherein selectively scanning the particle beam acrossthe scannable surface of the target comprises excluding the second path.6. The method of claim 1, wherein selectively scanning the particle beamacross the scannable surface of the target results in a neutron fluxthat is spatially uniform within the plane and falls within and isoptimized to an energy range for boron neutron capture therapytreatment.
 7. The method of claim 1, wherein the first pattern path andthe second path define the exclusion area of the target.
 8. The methodof claim 1, wherein the first pattern has a first half and a secondhalf, wherein the first and second halves are symmetrical.
 9. The methodof claim 1, wherein the first pattern has a start location and a stoplocation, wherein the start location is at or adjacent to the stoplocation.
 10. The method of claim 1, wherein the first radialorientation differs from the second radial orientation by 180 degrees.11. The method of claim 1, further comprising: scanning the particlebeam across the scannable surface of the target along a third path,wherein the third path forms the first pattern at a third radialorientation different from the first and second radial orientations. 12.The method of claim 1, wherein the first, second, and third radialorientations differ by 120 degrees.
 13. The method of claim 11, furthercomprising: scanning the particle beam across the scannable surface ofthe target along a fourth path, wherein the fourth path forms the firstpattern at a fourth radial orientation different from the first, second,and third radial orientations.
 14. The method of claim 13, wherein thefirst, second, third, and fourth radial orientations differ by 90degrees.
 15. The method of claim 13, further comprising: scanning theparticle beam across the scannable surface of the target along a fifthpath, wherein the fifth path forms the first pattern at a fifth radialorientation different from the first, second, third, and fourth radialorientations.
 16. The method of claim 15, wherein the first, second,third, fourth, and fifth radial orientations differ by 72 degrees. 17.The method of claim 1, wherein the first path corresponds to a firstinstance of a cycle, and the second path corresponds to a secondinstance of the cycle.
 18. The method of claim 17, wherein scanning ofthe first instance of the cycle and the second instance of the cycleforms a closed loop.
 19. The method of claim 1, wherein the particlebeam is a proton beam.
 20. A beam system comprising: a computing devicecomprising a processor communicatively coupled with memory, wherein thememory stores a plurality of instructions that, when executed by theprocessor, cause the processor to: control movement of a particle beamacross a scannable surface of a target along a first path, the particlebeam having a first flux while being scanned along the first path; andcontrol movement of the particle beam across the scannable surface ofthe target along a second path, the particle beam having a second fluxwhile being scanned along the first path, wherein the first pathcomprises a first pattern at a first radial orientation, and the secondpath comprises substantially the first pattern at a second radialorientation different from the first radial orientation, the second pathbeing within an exclusion area of the target, the second flux beinglower than the first flux.